Optimization of photoluminescence lifetime for ZnO films grown on ZnO substrates at low temperature

ZnO films were grown on Zn-polar ZnO substrates with 0.5° miscut toward the [1EQ \O(1,¯)00] direction by plasma-assisted molecular beam epitaxy (PAMBE). An atomically flat surface with one or two monolayer step height along the [0001] direction was achieved at low growth temperature. Wet etching of the substrates and ozone exposure reduced defects and improved photoluminescence (PL) lifetime by a factor of two. A 20 min interval between oxygen plasma ignition and growth was found necessary for excellent crystallinity and yielded high PL lifetimes of 0.179 ns. By decreasing the growth temperature in the low temperature range, the growth rate was increased from 0.02 μm/h to 0.246 μm/h, and correspondingly PL lifetime was improved by an order of magnitude, from 0.018 ns to 0.3 ns.

► ZnO homoepitaxial films were grown on Zn-polar ZnO substrates by PAMBE.
► Atomic flat surface with monolayer height steps was achieved at low growth temperature.
► Surface treatment was found crucial to remove the contaminations and improve PL lifetime.
► PL lifetime increases linearly with the increase of growth rate.
► PL lifetimes of up to 0.3 ns were achieved at low growth temperatures with proper surface preparation.